Rotary drying drum

ABSTRACT

Rotary drying drum for high-speed drying of thin webs such as paper or the like comprising a hollow cylinder mounted for rotation and adapted to receive a condensable fluid and discharge condensate. Improved heat transfer is obtained by spoiler bars positioned around the inner drum circumference generally parallel to the drum axis. The invention includes dividing these bars into segments and attaching each segment; a single fixture may be used for each segment and end contact with adjacent bar segments prevents the segments from rotational movement around the fixture point. As a result, performance is improved due to the ability of the bar segments to expand and flex with the drum&#39;&#39;s surface without excessive stress on the attaching fixtures.

United States Patent [191 Kraus ROTARY DRYING DRUM [75] Inventor: JamesJ Kraus, Neenah, Wis.

[73] Assignee: Kimberly-Clark Corporation,

Neenah, Wis.

[22] Filed: Dec. 26, 1972 [21] Appl. No.: 318,009

FOREIGN P TENTS OR APPLICATIONS 1,138,144 12/1968 Great Britain 165/81[111 3,808,700 4451 May 7,1974

Primary ExaminerJohn J. Camby Assistant Examiner-Henry C. Yuen Attorney,Agent, or Firm-Daniel J. Hanlon, Jr.; Raymond J. Miller; William D.Herrick 7] ABSTRACT Rotary drying drum for high-speed drying of thinwebs such as paper or the like comprising a hollow cylinder mounted forrotation and adapted to receive a condensable fluid and dischargecondensate. Improved heat transfer is obtained by spoiler barspositioned around the inner drum circumference generally parallel to thedrum axis. The invention includes dividing these bars into segments andattaching each segment; a single fixture may be used for each segmentand end contactwith adjacent bar segments prevents the segments fromrotational movement around the fixture point. As a result, performanceis improved due to the ability of the bar segments to expand and flexwith the drums surface without excessive stress on the attachingfixtures. v

4 Claims, 8 Drawing Figures 'PATENTEDHAY Y 1914 SHEET 2 OF 4 lWI. E] iiFIG.3

PATENTEDM 11914 FIG. 4

SHEET 3 OF 4 FIGS FIG.6

FIG.7

PATENTED M 7 I97 SHEET B [If 4 FIG. 8

BACKGROUND OF THE INVENTION The invention relates to dryer drumsparticularly adaptable for papermaking machines. The drying section of apapermaking machine generally includes a series of dryer drums, each ofwhich has a cylindrical shell, spaced heads extending across the shellto close the open ends thereof, journals for rotatively mounting theshell, conduits for introducing a condensable fluid into the shell andconduits forwithdrawing condensate from the shell. The paper web travelsfrom one of these dryer drums to the others in such a drying section.Particularly for lightweight paper webs, a single so-called Yankee dryerdrum is utilized. A Yankee dryer drum also comprises a cylindrical shelland spaced heads and is generally of the same construction as the dryerdrums previously mentioned; however, a Yankee dryer drum is ordinarilyof substantially greater diameter, and onlyone of these drumsisgenerallyused in a'papermaking machine. However, with either type ofdrum, the smaller type or the large Yankee type,'there are certainoperating limitations due to the collection of condensate in the drum.

The interior of such a dryer drum has a condensable fluid (usuallysteam) admitted to it so that the dryer shell is heated for drying paperweb traveling over the shell. Condensate forms within the shell as thefluid gives off its heat tothe shell; and, at low speeds, the condensatepools within the bottom part of the drum. At higher peripheral speeds,such as above 1,000 feet per minute at which most of the drumsarepresently run, the condensate rims within the dryer shell, tending tocollect in a cylindrical layer about the complete internal periphery ofthe shell, Although the condensate layer is at the temperature of thefluid generally, heat transfer through the condensate layer isrelatively slow since the body of condensate within the drum keeps thefluid away from direct action on the dryer shell. Thus, as these dryerdrums are ordinarily operated, the layer of condensate within the dryershell is kept at a minimum thickness for maximum heat transfer.

It has also been found that, in addition to the rimming effect of thecondensate at higher dryer speeds, the

condensate also oscillates circularly about the internal surface of thedrum. The cause of the oscillation is the force of gravity whichalternately retards and accelerates' the condensate ring within thedrum.

The periodical Das Papier," Vol. 14, No. 10a, of October, 1960 (pages600 -609), in an article written by Barnscheidt and Schadler, gives adescription of this oscillating movement of condensate in a steam heatedcylinder or dryer drum, and the authors of this article describe thereinthe use of rails or bars within the drum for increasing condensateturbulence to increase heat flow through the condensate. These bars(also the subject of USP No. 3,217,426 to Barnscheidt and Staud) arespaced on approximately 10 inch centers. According to the article, therails cause a surface wave associated with oscillation of the condensatewithin the dryer shell, and Branscheidt and Schadler apparently indicatein their patent that resonating conditions are undesirable and may beavoided by spacing the bars at unequal peripheral distances. The authorsconclude atbars r m r o .9.3inshJi l1 w rabsstin their dryer.

In US. Pat. No. 3,724,094 assigned to the assignee' of the presentinvention, Appel and Hong describe an improved drying drum arrangementin which the bars are attached in a specific configuration to produceresonating conditions in the condensate. In this manner, a greaterdegree of turbulence is introduced in the condensate layer, and heattransfer even further increased.

However, the present invention is directed to a further improvement inthe operation of such drying drums.'The bars are generally thinner thanthe dryer shell and, since they are first contacted by the hot steam,they tend to expand more rapidly than the shell. Additionally, inmostcases, the dryer drum is operated in a nip configuration with apressure roll. This pressure roll causes radial deflection of the drumsurface and contributes to loosening of the bars, particularly near theends. In either event, the damage done if a bar becomes loose within arotating drum can cause extended periods of downtime for replacement ofthe dislodged bar.

SUMMARY OF THE INVENTION Briefly, in accordance with the presentinvention, there is provided a rotary drying drum especially adapted forpapermaking machines and having spoiler bars extending axially andattached to the internal drum periphery. In particular, the presentinvention is directed to an improved segmented bar structure which canbe attached by a single attachment means per segment and provides forsome degree of bar flexing with the dryer surface as well as thermalexpansion of the segments. Rotational movement of the bar segments aboutthe single attachment means is inhibited by contact with the ends ofadjacent bar segments. The result is improved dryer operation forextended periods with a minimum amount of downtime and fewer incidencesof bar dislodgement.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section viewof a Yankee dryer drum having aseries of condensate impeding bars fixedon the inner surface;

FIG. 2 is a sectional view taken on line 2-2 of FIG. 1-

FIG. 7 is a top view of the embodiment shown in FIG.

FIG. 8 is a fragmentary side elevational view of a section of apapermaking machine incorporatingthe dryer drum illustrated in thepreceding figures.

FIG. 3 is 'a sectional view taken on line 3-3 of FIG.

Like characters of reference designate like parts in the several views.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in FIG. 1, thedryer drum comprises a thin cylindrical outer shell and a pair ofrelatively flat ring-shaped heads 11 and 12. The heads 11 and 12 arerigidly secured to the ends of the shell 10 and are supported by ahollow central axle or shaft 13. An integral bolting flange .14 isprovided at each end of the shell 10, and each flange mates with asimilar peripheral flange 15 on the adjacent head. The rigid attachmentof the shell to each head may be made by a plurality of bolts 16inserted from the insideof the shell and drawn up by nuts on the outsideof the head.

A short cylindrical section 17 has a machined bolting flange 18 providedat its inner end and is formed integrally with each of the heads 11 and12, each section extending longitudinally of the shell 10 and at aradial location which is intermediate the inner and outer edges of thehead. A plurality of heavy staying members 19 extend between the heads11 and 12 longitudinally of the dryer, being fixed with respect to theflanges 18 by means of flanges 20 formed on the staying members 19 andbolts 21 extending through the flanges 18 and 20. The staying members 19control the bowing of the heads 11 and 12 to eliminate stress occurringin the shell 10 at or near its connections to the heads 11 and 12.

The heads 11 and 12 and shell 10 and the central shaft 13 are of castconstruction. The shaft 13 is formed in two halves 22 and 23, and thehalves are provided with flanges 24 and 25, with bolts 26 extendingthrough the flanges to fix the halves 22 and 33 together. Two separatecompartments 27 and 28 are provided within the shaft 13 by means of aseparator 29 within the half 22. An enlarged bolting flange 30 isprovided near each end of the shaft 13, and each head 11 and 12 isprovided with a flange 31 that mates with a flange 30, the flanges 30and 31 being fixed together by means of bolts 32. Journals 33 areprovided on the ends of the shaft 13 for rotatably supporting the dryerin suitable bearings, and a shaft extension 34 is provided at one end ofthe shaft 13 for mounting a driving gear or sprocket or the like. Bores35 and 36, respectively, in communication with the compartments 27 and28, are provided in the shaft 13 at its ends. Bores 35 and 36 mayrespectively be'utilized to provide steam or other condensable fluidsunder pressure into the compartment 27 and for withdrawing thecondensate from the compartment 28.

A plurality of steam supply pipes 37 having rows of steam dischargeopenings 38 in them may be used for supplying steam under pressure tothe interior of the dryer drum. The pipes 37 are connected to thecompartment 27, and the pipes 37 extend axially with respect to theshaft 13 and may be appropriately fixed adjacent their ends to the shaft13.

The dryer is provided with a condensate withdrawal system whichcomprises a pair of manifolds 39 and 40 positioned oppositely from eachother with respect to the shaft 13 and located adjacent the innersurface of the shell 10. The manifolds 39 and 40 are supported at theirends from the bolting flanges 18 by means of supports 41 and aresupported intermediate their ends from the staying members 19 by meansof ties 42.

A plurality of equal length small diameter tubes.43 (FIG. 3) extendradially through each of the manifolds 39 and 40. The tubes 43 havetheir outer ends 44 terminating closely adjacent the inner surface ofthe shell 10 and have their inner ends 45 terminating well within theassociated manifold close to the longitudinal center of the manifold.

The manifold 40 has a pair of arcuately shaped branch pipes 46 and 47(FIG. 2) connected with it, and the manifold 39 has a pair of similarpipes 48 and 49 connected with it. The pipes 46 and 48 are connectedtogether by means of a Y-shaped fitting 50, and the central leg of thefitting 50 is connected'by means of a radially extending pipe 51 withthe shaft 13 and particularly with the compartment 28 in the shaft. Thepipes 47 and 49 are connected similarly with the compartment 28utilizing a Y-shaped fitting 52 connected to a radially extending pipe53. The branch pipes 46, 47, 48 and 49 are supported intermediate theirends by means of support brackets 54 extending between adjacent stayingmembers 19 and tie rods 55 extending between the brackets 54 and thepipes 46, 47, 48 and 49.

A plurality of bars, A, B, C, D, E, F, G, H, I, J, K, L,

etc., are longitudinally disposed within the shell 10 and are fixed tothe internal shell surface. In accordance with the present invention,each of the bars, A, B, C, etc. is divided into segments and eachsegment fixed by means of a single attachment means 56 extending throughthe bar to the shell 10 as will be described in detail with reference tothe later drawings. A manhole 57, closed by a removable cover 58, isprovided in each of the heads 11 and 12 so that workmen may enter thedryer drum when it is stationary and unheated for the purpose of fixingthe bars A, B, C, etc., within theshell l0.

The dryer drum may be mounted in a papermaking machine as illustrateddiagrammatically in FIG. 8. The journals 33 of the shaft 13 may bemounted in bearings 59 which are secured to a supporting frame 60. Thewet paper web to be dried is carried by a felt web 61 which travelsaround felt rolls 62. The paper web is forced against the surface of thedryer shell 10 by a pressure roll 63 which is rotatably mounted inbrackets '64 attached to arms 65. The arms 65 are each pivoted at.66 tothe frame 60, and the pressure roll 63 is forced against the surface ofthe dryer shell 10 by a hydraulic or pneumaticactuator 67 which bearsagainst each arm I The dried paper web may be removed from the surfaceof the dryer shell by a creping doctor which includes a doctor blade 68secured within a doctor blade holder 69. The blade 68 and holder 69 maybe supported by conventional mechanism including shafts 70 carried bythe supporting frame 60 and rotatably mounted within'guide blocks71. Theblocks 71 in turn are slidably mounted within a slide assembly 72attached to a pivot frame 73 carried by the frame 60. Through the slidearrangement provided by the guide block 71 and slide assembly 72, thevertical position of the doctor blade 68 can be varied as desired toobtain the best creping angle. The doctor blade holder 69 and the blade68 are pivoted from a toggle mechanism 74 which is attached through alever arm 75 to one of the shafts 70. A spring loading mechanism 76 isconnected through the toggle mechanism 74 to provide a resilient contactfor the doctor blade against the surface of the dryer shell 10.

In operation, a moist paper'web is directed onto the outer surface ofthe shell 10, being carried by the felt web 61; and the pressure roll63, which exerts a substantial pressure on and has a pressure nip withthe dryer drum, forces the paper web against the outer surface of theshell and causes the paper web to adhere onto the shell 10. A sprocketor other driving mechanism (not shown) on the extension 34 may beutilized for drivingly rotating the dryer drum. The web is dried as thedrum rotates, and the web is creped off the outer surface of the drum bymeans of the creping blade 68. Alternatively, the paper web may besimply pulled off the surface of the dryer drum without the use of sucha blade.

Steam under pressure is supplied to the compartment 27 through the bore35, and the steam enters the internal compartment of the drum throughthe supply pipes 37 and the openings 38 in the pipes 37. The steam heatsthe dryer drum for drying the paper web; and, as the steam loses heat,it condenses into water. The water condensate remains on the internalsurface of the shell 10 and rims or lies completely around the shell dueto the action of centrifugal force. The condensate removal systemincluding the manifolds 39 and 40, the small diameter tubes 43 and thecondensate withdrawal pipes 46, 47, 48,49, 51 and 53 remove thiscondensate.

The tube ends 44 are located very close to the internal surface of theshell 10, and steam within the dryer drum rushes to these ends of thetubes, since the pressure within the tubes and in the connectedmanifolds 39 and 40 is lower than the pressure of the steam within. thedrum. The steam, in entering the ends 44 of the tubes 43, sweeps acrossthe inner surface of the dryer drum and atomizes the condensate existingon the inner drum surface. Thus, a steam-water mixture passes radiallyinward through the bores of the tubes 43 into the manifolds 39 and 40.

Some of the steam condenses as it passes through the tubes 43, but thepressure of the steam within the dryer drum is sufficient to move thewater-steam mixture inward and some condensation takes place also withinthe manifolds 39 and 40. The water condensate tends to collect on theouter walls of the manifolds 39 and 40 and moves from these outer wallsinto the pipes 46, 47, 48 and 49 and from these last mentioned pipesinto the compartment 28 through the fittings 50 and 52 and the radiallyextending pipes 52 and 53.

The steam condensate withdrawal system is substantially that disclosedin Joseph B. Webb US. Pat. No. 3,359,647; and this patent may bereferred to for more details of the withdrawal system. Of course, theinvention is not limited to use in combination with any particularcondensate removal system, and others such as scoops or dippers may beutilized as well.

Assuming that the dryer drum is rotating at relatively high speeds, suchas 1,000 feet per minute peripheral speed or greater, the dryercondensate tends to rim the drum completely around the drum; and thisrimming is accompanied by oscillation of the condensate circularly aboutthe internal surface of the drum. This oscillation is apparently causedby the force of gravity, alternately retarding and accelerating thewater ring within the drum. As the water ring oscillates in-the drum, itflows over the bars A, B, C, D, etc.; and these coefficient (BTUs perhour per square foot per degree Fahrenheit) from the steam through thedryer shell 10. The condensate layer thus rendered turbulent is reducedfrom a uniform thickness layer to one that is of very non-uniformthickness, allowing greater heat transfer; and, in addition, theturbulent flow of the condensate apparently scrubs off a water film fromthe interior surface of the dryer which action contributes to theincrease in heat transfer. The height of the various bars, A, B, etc.,is preferably maintained sufficiently small so that the condensatesloshes over the bars, not only for increasing the turbulence but alsofor allowing the condensate to flow to to the tubes 43 which aredisposed in two opposite longitudinal rows on the internal surface ofthe drum.

The separation of the bars peripherally within the shell 10 ispreferably determined in accordance with the aforementioned Appel/I-Iongpatent. In this manner resonance of sloshing in the spaces between thebars A,

B, C, etc., occurs so that the condensate rises to a maxi-' mum heightat the bars. Preferably a minimum average thickness of condensate isused in the drum, inasmuch as the condensate is a poor conductor ofheat; and it is contemplated that the average condensate thickness shallbe within the range of about 1 to 7 1/2 millimeters and preferably aboutone millimeter.

Turning now to FIGS. 4 and 5, one embodiment of the improved bars andattachment-of the present invention will be described. As shown therein,each bar A, B, C, etc., is composed of a plurality of segments a, b, 0,etc. These segments are each attached to outer shell 10 by a singlefastener 56 placed near the center of the segment and which may be ascrew, as illustrated. Additional fasteners may, of course, be used ifdesired. To maintain the segments in alignment, each end is in contactwith the end of an adjacent segment. In this embodiment, each segment,excluding of course the end ones, has a tongue 77 on one end and amatching groove 78 in the opposite end. The tongue of one segment fitsinto the groove of the adjacent segment so that a substantiallycontinuous bar is formed. This tongue and groove, segmented arrangementallows some flexing in the drum radial direction along with the drumsurface so that undue stress is not placed on the fasteners. It is alsopreferred that some length clearance be provided for individual segmentthermal expansion by making the groove slightly longer than the tongue.As illustrated, the end segments are preferably somewhat shorter thanthe others so that the attachment is placed closer to'the free ends ofthe bar.

The bars are generally thinner than the dryer shell and, since they arefirst contacted by the hot steam, they tend to expand more rapidly thanthe shell. By dividing the bars into segments and making the groovesslightly longer than the corresponding tongues, this increased expansionis easily accomodated by the present invention.

FIGS. 6 and 7 illustrate an alternative embodiment. In this case,instead of machining or otherwise forming a tongue and groove into theends of the individual segments, the ends of adjacent segments areplaced in slightly overlapping and abutting position as illustrated.Thus, while the segments are not in strict alignment, the individualsegments are prevented from rotation about the axis of the fastener bycontact with the ends of adjacent segments. Because of the necessity toinstall the segments in strictly parallel positions, this embodiment issomewhat less preferred.

While it is not critical to the present invention, it is preferred thatthe bar segment be in the range of from 7 to ll inches in lengthdepending upon factors such as the overall width of the machine, and thediameter of the dryer cylinder. With respect to the height of the bars,A, B, C, etc., the analysis does not indicate any particular optimumheight, but an approximate desirable range can be identified. When thebars are spaced such that sloshing occurs at or near resonant frequencyfor the waves in the spaces between the bars A, B, etc., then the fluidrises up first at one end of the space and then at the other end. Theheight of the mass of condensate when it sloshes against either side ofeach bar should be greater thanthe height of the bar so that some of thecondensate spills over the bar into the next space, and this spillagecauses the condensate to migrate around the internal surface of theshell toward the condensate withdrawal tubes 43, assuming that between25 to 50% of the condensate originally in the space between adjacentbars A, B, etc., spills over a bar into the next space. For thesepurposes, it has been found that the bar height should be between 1.5and 7.5 times the average'condensate depth in the dryer; and it ispreferred that the bar height should be between 2 and 3 times theaverage condensate depth for rapid migration of condensate in the dryer,although substantial improvement in heat transfer can be expected forbar heights between 1.5 and 4 times the average condensate depth.

It will be understood that the average condensate depth can be regulatedby moving the outer ends 44 of the tubes 43 toward and away from theinternal surface of the shell 10; and preferably the tube ends 44 shallbe located so close to the internal surface of the shell 10 that theaverage condensate depth is no greater than 3 millimeters, inasmuch asthicker condensate layers would cause an unduly great retardation ofheat flow. Due to the possibility of hot spots near the ends 44 of theindividual siphon tubes 43, it is preferred that the condensate depthsused shall not be less than 1 millimeter.

Since the average condensate depth is preferably between 1 millimeterand 3 millimeters, the permissible bar heights mentioned above arebetween 1.5 millimeters and 22.5 millimeters, more preferably between1.5 millimeters and 12 millimeters, and still more preferably between 2millimeters and 9 millimeters. These heights correspond, respectively,to the range of 1.5 to 7.5, the range of 1.5 to 4 and the range of 2 to3 times the average condensate depth mentioned above. For furtherdescription and illustration of the condensate behavior within the dryerdrum, reference may be had to the aforementioned Appel/Hong patent.

The width of the bars A, B, etc. is quite immaterial insofar as thecondensate motion within the dryer shell is concerned; however, if a baris too wide, it will have an undesirable insulating effect with respectto the outer shells surface which may produce a wet streak inthe paperbeing dried. Each of the bars A, B, etc. should, therefore, beconsiderably narrower than the thickness of the dryer shell. The dryershell may have a thickness of from 1 1/4 inches to 2 inches, forexample, and the width of the bar may thus well be one half inch or lessand should preferably be 3/8 inch 'to 1/2 fore not limited to anyspecific bar spacing but will have advantages in the devices describedby Barnscheidt et al aswell.

Although the improved dryer drum of the present invention has beenderibed in connection with a source of steam for heating the drum, itmay also be used with other condensible heating fluids; for example,with Dowtherm E and Dowtherm'A which are particularly described in US.Pat. No. 3,363,328 for Rotary Drying Drum, issued Jan. 16, 1968, to Hongand Dickens. As is mentioned in said prior US. Pat. No. 3,363,328,particularly in col. 2, lines 27 to 59 of the patent, these fluidstermed Dowtherm E and Dowtherm A have higher condensing temperaturesthan water and may thus supply more heat to a dryer drum.

Thus, it is apparent that there has been provided in accordance with theinvention, an improved rotary drying drum that fully satisfies theobjects, aims, and advantages set forth above. While the invention hasbeen described in connection with specific embodiments thereof, it isevident that many alternatives, modifications, and variations will beapparent to those skilled in the art in light of the foregoingdescription. Accordingly, it is intended to embrace all suchalternatives,

modifications, and variations as fall within the spirit and broad scopeof the appended claims.

I claim:

, 1. In a rotary drying drum having journals for mounting the drum, aconnection for supplying a condensible fluid, a condensate removalconnection for removing condensate out of the drum, and a plurality ofbars extending lengthwise of the drum and disposed on the inside surfaceof the drum for giving turbulence to the condensate in the drum,

the improvement wherein said bars are comprised of segments which areattached to the inside surface of the drum and maintained in position bycontact with the ends of adjacent segments, each of substantially all ofsaid segments being attached by a single fixture.

2. The rotary drying drum of claim 1 wherein the contact between theends of adjacent bar segments is maintained by providing a tongue on theend of onebar 4. The rotary drying drum of claim 1 wherein the contactwith the ends of adjacent bar segments is provided by staggeringadjacent segments and overlapping the segments so that the ends ofadjacent bars contact each other.

l l l 4 222 3 UNITED STATES PATENT OFFICE 3 I CERTIFICATE OF CORRECTION?atent No. 3I-808-r700 Dated May 7, 1974 Inventor(s) James J. Kraus Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

"'1 Column 1 line 37, delete the comma, Column 2, line 4, "Branscheidt"should, read Barnscheidt Column 3, line 35, "33" should read 23 Column5, line .48-, "52" should read 51 Signed and sealed this 1st day ofOctober 1974.

- (SEAL) Attest:

5 McCOYM'. GIBSON-JR. C.'MARSML DANN Attesting Officer Commissioner ofPatents

1. In a rotary drying drum having journals for mounting the drum, aconnection for supplying a condensible fluid, a condensate removalconnection for removing condensate out of the drum, and a plurality ofbars extending lengthwise of the drum and disposed on the inside surfaceof the drum for giving turbulence to the condensate in the drum, theimprovement wherein said bars are comprised of segments which areattached to the inside surface of the drum and maintained in position bycontact with the ends of adjacent segments, each of substantiaLly all ofsaid segments being attached by a single fixture.
 2. The rotary dryingdrum of claim 1 wherein the contact between the ends of adjacent barsegments is maintained by providing a tongue on the end of one barsegment which substantially matches a groove in the end of the adjacentbar segment.
 3. The rotary drying drum of claim 2 wherein the groove isslightly longer than the corresponding tongue to provide for thermalexpansion of the bar segments.
 4. The rotary drying drum of claim 1wherein the contact with the ends of adjacent bar segments is providedby staggering adjacent segments and overlapping the segments so that theends of adjacent bars contact each other.